My Christmas cracker jokes seem to have got particularly topical thisyear...Two bacteria walk into a bar. The bartender says, "Get out! We don't serve any bacteria in this bar. The two bacteria say, "Hey, but we work here. We're staph."

Staphylococcus aureus is a common bacteria found on the skin of all human beings and up the noses of 30% of the population. The antibiotic Methicillin (Meticillin internationally) was first described in 1961 and two years later licensed in the UK to treat S. aureus. By the mid 1970s about 2% of hospital acquired S. aureus infections were resistant to Methicillin and labelled Methicillin Resistant Staphylococcus aureus (MRSA). By the mid 1990s hospital acquired MRSA had reached about 50%.Despite being common for over 20 years, MRSA still seems to cause confusion amongst doctors. So what is MRSA, why did it become notorious and how do you get the treatment right?What is MRSA?MRSA is S. aureus which has acquired a gene called MecA. This gene encodes for a type of Penicillin Binding Protein (PBP). The traditional treatments for S. aureus are the Beta-lactam antibiotics such as Flucloxacillin (a derivative of Meticillin). However these normal Beta-lactam antibiotics can’t bind to this protein and therefore are ineffective. The presence of the MecA gene makes MRSA resistant to all of the regularly used Beta-lactams (see below).

Click on image to enlarge

To make matters worse, the MecA gene got into a particular strain of S. aureus which is already resistant to quinolones, macrolides and lincosamides. So in addition to not being able to use any Beta-lactams to treat MRSA, you also can’t use Ciprofloxacin, Erythromycin or Clindamycin either! The table below shows the normal resistance and sensitivity pattern that can be predicted for an MRSA in the UK.

Why did it become notorious? Consider this...back in the 1980s a surgeon would uncover the dressings of 5-6 patients on a post-op ward round without cleaning their hands in-between, possibly unthinkable today but the infection control messages were not so stringent. If the first patient had MRSA (something that was not screened for back in the 1980s) then the next 4-5 patients would be exposed to and potentially become colonised with MRSA.

As S. aureus is a common cause for multiple infections, the possibility of a resistant strain being present and transferred due to the lack of infection control ensured MRSA became established in hospitals. Both the government and media coined the term “superbug” and MRSA became synonymous with poor cleanliness and substandard care and became the “scapegoat” or “poster boy” for all antibiotic resistance.

How do you get the treatment right?If a patient who has previously tested positive for MRSA (check earlier results and clinical history) develops an infection for which S. aureus is a common cause (e.g. cellulitis, septic arthritis, osteomyelitis as well as serious infections such as sepsis and epidural abscesses) then choose an antibiotic that covers for MRSA as the patient is likely to remain colonised even after receiving decolonisation or suppression therapy. Not choosing an antibiotic that covers for MRSA would be considered bad practice as demonstrated by the actions of both the General Medical Council (GMC) and also the Law Courts. In 2000, two junior doctors failed to treat MRSA in a 31 year old post operative orthopaedic patient. They also failed to recognise how sick their patient was and therefore did not escalate to a senior colleague, which resulted in the patient dying. The doctors were suspended by the GMC and received 2 year suspended prison sentences for manslaughter. So the message should be clear, MRSA is a common problem and ALL doctors should be familiar with its management. REMEMBER, if a patient is or has been MRSA positive in the past and develops an infection likely to be caused by S. aureus then it would be considered negligent if the MRSA is not covered by the initial antibiotics.